1. Field of the Invention
The present invention relates in general to a rotary cutting tool, and more particularly to improvements in such a rotary cutting tool having at least one peripheral cutting edge each of which includes a corrugated edge portion in the form of a roughing cutting edge portion or a nicked cutting edge portion.
2. Discussion of the Related Art
As one type of a rotary cutting tool which is to be rotated about its axis for machining or cutting a workpiece with its peripheral cutting edges, there is known a tapered end mill in which the diameter of the peripheral cutting edges is changed gradually in the axial direction. Such a tapered end mill is widely used for formation of a rib slot in a die or mold, cutting of a side face in a die or mold, or other kinds of machining works. There is proposed an end mill having, in each of its cutting edges, a corrugated edge portion which serves for breaking a cutting chip into small pieces and accordingly reducing a cutting resistance so as to improve cutting performance and cutting efficiency of the end mill, as disclosed in JP-A-H7-299635 (publication of unexamined Japanese Patent Application laid open in 1995) and JP-A-H9-29530 (publication of unexamined Japanese Patent Application laid open in 1997). The corrugated edge portion takes, for example, the form of a roughing cutting edge portion having sinuous shape in which the diameter is gradually changed in the axial direction, or the form of a nicked cutting edge portion in which a plurality of nicks are formed to be arranged with a constant spacing interval in the axial direction. Whichever the corrugated edge portion takes the form of the roughing cutting portion or the form of the nicked cutting edge portion, it can be said that the corrugated edge portion has, in its cross section taken in a plane containing a rake face which cooperates with a flank face to define the corresponding cutting edge, a corrugated shape consisting of a succession of protrusions and recesses which are alternately arranged. The pitch, depth and other dimension of the corrugated shape of the roughing cutting edge portion or nicked cutting edge portion are determined to have suitable amounts, commonly, in view of the diameter of a body portion in which the cutting edges are formed. When the diameter of the body portion is generally small, such dimensions of the corrugated shape of the roughing or nicked cutting edge are adapted to be small, so that the pieces into which the cutting chip is broken by the roughing or nicked cutting edge portion is sufficiently small. This is because the rigidity of the end mill is relatively small when the diameter of the body portion is relatively small.
The pitch, depth and other dimensions of the corrugated shape of the roughing or nicked cutting edge are held constant throughout the entire length of the corrugated edge portion of the cutting edge, even where the end mill is of a tapered end mill in which the diameter of the body portion is changed in the axial direction. That is, the dimensions of the corrugated shape of the corrugated edge portion of a tapered end mill are determined, for example, on the basis of the diameter of an axially intermediate portion of the body portion of the tapered end mill. However, the thus determined dimensions of the corrugated shape do not necessarily enable, particularly, axially opposite end portions of the body portion to exhibit a sufficient improvement in their cutting performance, in spite of the provision of the corrugated edge portion in the cutting edge. Namely, where the dimensions of the corrugated shape are determined on the basis of the diameter of the axially intermediate portion of the body portion, a sufficiently improved cutting performance is not necessarily exhibited by the axially opposite end portions of the body portion in which the diameter is increased and reduced, thereby undesirably reducing a degree of freedom in determining number of revolutions, feed rate and other cutting conditions which are applicable to the end mill.
It is therefore an object of the present invention to provide a rotary cutting tool which has a corrugated edge portion in the form of a roughing cutting edge portion or a nicked cutting edge, and which exhibits a sufficiently improved cutting performance in the entire axial length of each cutting edge irrespective of the change of diameter of the cutting edge. The object may be achieved according to any one of first through ninth aspects of the invention which are described below.
The first aspect of this invention provides a rotary cutting tool which is to be rotated about an axis thereof for cutting a workpiece, comprising: a generally cylindrical body portion having (a) at least one flute each of which is formed in the cylindrical body portion and each of which extends from an axially distal end of the cylindrical body portion toward an axially proximal end of the cylindrical body portion, and (b) at least one cutting edge each of which is provided by one of widthwise opposite edges of the flute, wherein each of the above-described at least one cutting edge includes a corrugated edge portion having a corrugated shape, and wherein at least one of a pitch and a depth of the corrugated shape is increased with an increase in a diameter of the cylindrical body portion whose outer circumferential surface is defined by a rotary trajectory of an envelope passing through crests of the corrugated shape.
The above-described corrugated shape may consist of a succession of protrusions and recesses which are alternately arranged. Each of the crests or peaks is defined as the highest point of a corresponding one of the protrusions. The pitch is defined as a distance between the crests or peaks of two successive protrusions, or between roots or bottoms of two successive recesses. The depth is defined as a distance between the crest and root which are adjacent to each other. It is noted that the cylindrical body portion includes a diameter changing portion whose diameter is changed in the axial direction.
According to the second aspect of the invention, in the rotary cutting tool defined in the first aspect of the invention, the generally cylindrical body portion includes a tapered body portion, so that the diameter of the cylindrical body portion is increased in a direction away from one of the axially distal and proximal ends of the body portion toward the other of the axially distal and proximal ends of the body portion. In the rotary cutting tool of this second aspect of the invention, the cylindrical body portion includes the above-described diameter changing portion in the form of the tapered body portion.
According to the third aspect of the invention, in the rotary cutting tool defined in the first or second aspect of the invention, the pitch of the corrugated shape is increased with the increase in the diameter of the cylindrical body portion such that the following expression (1) is satisfied:
0.5+(3/100)xc3x97Dxe2x89xa6Pxe2x89xa62+(3/25)xc3x97Dxe2x80x83xe2x80x83(1); 
wherein D represents the diameter of the cylindrical body portion; and P represents the pitch of the corrugated shape. It is noted that the pitch represents a distance measured along a generating line of the diameter changing portion or tapered body portion, between the crests or peaks of two successive protrusions, or between the roots or bottoms of two successive recesses, whichever each of the above-described at least one flute consist of a straight flute or a helical flute.
The fourth aspect of this invention provides a rotary cutting tool which is to be rotated about an axis thereof for cutting a workpiece, comprising: a generally cylindrical body portion having (a) at least one flute each of which is formed in the cylindrical body portion and each of which extends from an axially distal end of the cylindrical body portion toward an axially proximal end of the cylindrical body portion, and (b) at least one cutting edge each of which is provided by one of widthwise opposite edges of the flute, wherein each of the above-described at least one cutting edge includes a roughing cutting edge portion having a corrugated shape consisting of a succession of protrusions and recesses which are alternately arranged, each of the protrusions having a first radius of curvature while each of the recesses having a second radius of curvature, and wherein at least one of a pitch of the corrugated shape, a depth of the corrugated shape, the first radius of curvature and the second radius of curvature is increased with an increase in a diameter of the cylindrical body portion whose outer circumferential surface is defined by a rotary trajectory of an envelope passing through crests of the corrugated shape.
The above-described roughing cutting edge portion can be formed, for example, by forming a plurality of grooves in the flank face such that the grooves are arranged along each of the above-described at least one cutting edge with a predetermined spacing interval between two successive grooves.
According to the fifth aspect of the invention, in the rotary cutting tool defined in the fourth aspect of the invention, the generally cylindrical body portion includes a tapered body portion, so that the diameter of the cylindrical body portion is increased in a direction away from one of the axially distal and proximal ends of the body portion toward the other of the axially distal and proximal ends of the body portion.
According to the sixth aspect of the invention, in the rotary cutting tool defined in the fourth or first aspect of the invention, the pitch of the corrugated shape is increased with the increase in the diameter of the cylindrical body portion such that the following expression (2) is satisfied:
0.5+(3/100)xc3x97Dxe2x89xa6PRxe2x89xa62+(3/25)xc3x97Dxe2x80x83xe2x80x83(2); 
wherein D represents the diameter of the cylindrical body portion; and PR represents the pitch of the corrugated shape. It is noted that the pitch represents a distance measured along a generating line of the diameter changing portion or tapered body portion, between the crests or peaks of two successive protrusions, or between the roots or bottoms of two successive recesses, whichever each of the above-described at least one flute consist of a straight flute or a helical flute.
The seventh aspect of this invention provides a rotary cutting tool which is to be rotated about an axis thereof for cutting a workpiece, comprising: a generally cylindrical body portion having (a) at least one flute each of which is formed in the cylindrical body portion and each of which extends from an axially distal end of the cylindrical body portion toward an axially proximal end of the cylindrical body portion, and (b) at least one cutting edge each of which is provided by one of widthwise opposite edges of the flute, wherein each of the above-described at least one cutting edge includes a nicked cutting edge portion having a corrugated shape, and wherein at least one of a pitch and a depth of the corrugated shape is increased with an increase in a diameter of the cylindrical body portion whose outer circumferential surface is defined by a rotary trajectory of an envelope passing through crests of the corrugated shape.
The above-described nicked cutting edge portion can be formed, for example, by forming a plurality of nicks or grooves in the flank face such that the nicks or grooves are arranged along each of the above-described at least one cutting edge with a predetermined spacing interval between two successive nicks or grooves.
According to the eighth aspect of the invention, in the rotary cutting tool defined in the seventh aspect of the invention, the generally cylindrical body portion includes a tapered body portion, so that the diameter of the cylindrical body portion is increased in a direction away from one of the axially distal and proximal ends of the body portion toward the other of the axially distal and proximal ends of the body portion.
According to the ninth aspect of the invention, in the rotary cutting tool defined in the seventh or eighth aspect of the invention, the pitch of the corrugated shape is increased with the increase in the diameter of the cylindrical body portion such that the following expression (3) is satisfied:
0.5+(3/100)xc3x97Dxe2x89xa6PNxe2x89xa62+(3/25)xc3x97Dxe2x80x83xe2x80x83(3); 
wherein D represents the diameter of the cylindrical body portion; and PN represents the pitch of the corrugated shape. It is noted that the pitch represents a distance measured along a generating line of the diameter changing portion or tapered body portion, between the crests or peaks of two successive protrusions, or between the roots or bottoms of two successive recesses, whichever each of the above-described at least one flute consist of a straight flute or a helical flute.
In the rotary cutting tool defined in any one of the first through third aspects of the invention in which at least one of the pitch and depth of the corrugated shape of the corrugated edge portion is increased with the increase in the diameter of the cylindrical body portion, the corrugated shape can be adapted to have dimensions suitable for the diameter throughout an entire axial length of the corrugated edge portion. This arrangement enables the rotary cutting tool to exhibit a sufficiently improved cutting performance in the entire axial length of each cutting edge irrespective of the change of the diameter of the cylindrical body portion, thereby enabling the rotary cutting tool to cut a workpiece with an increased rate and an increased depth of cut.
In the rotary cutting tool defined in any one of the fourth through sixth aspects of the invention in which at least one of the pitch, depth, first radius of curvature and second radius of curvature of the corrugated shape of the roughing cutting edge portion is increased with the increase in the diameter of the cylindrical body portion, the corrugated shape can be adapted to have dimensions suitable for the diameter throughout the entire axial length of the roughing cutting edge portion. This arrangement provides substantially the same technical advantages as those provided by the arrangement of each of the first through third aspects of the invention.
In the rotary cutting tool defined in any one of the seventh through ninth aspects of the invention in which at least one of the pitch and depth of the corrugated shape of the nicked cutting edge portion is increased with the increase in the diameter of the cylindrical body portion, the corrugated shape can be adapted to have dimensions suitable for the diameter throughout the entire axial length of the nicked cutting edge portion. This arrangement also provides substantially the same technical advantages as those provided by the arrangement of each of the first through third aspects of the invention.
In the rotary cutting tool defined in any one of the third, sixth and ninth aspects of the invention in which the pitch of the corrugated shape is increased with the increase in the diameter of the cylindrical body portion such that the above-described expression (1), (2) or (3) is satisfied, it is possible to more reliably exhibit a sufficiently improved cutting performance in the entire axial length of each cutting edge irrespective of the change of the diameter of the cylindrical body portion.
The present invention is preferably applied to an tapered end mill in which the cylindrical body portion having the cutting edge or edges formed therein consists a tapered body portion. However, the invention is applicable also to a formed end mill such as a so-called xe2x80x9cChristmas-tree cutterxe2x80x9d in which the body portion has at least one large diameter portion and at least one small diameter portion which are alternately arranged in the axial direction so as to have a Christmas-tree-like configuration. That is, the invention is applicable to any rotary cutting tool as long as the cylindrical body portion of the cutting tool includes a diameter changing portion whose diameter is changed in the axial direction. Further, although it is preferable that each of the above-described at least one flute may consist of a helical flute extending in a helical direction which is inclined or twisted with respect to the axis of the cylindrical body portion by a predetermined angle so that the above-described at least one cutting edge extends in the helical direction, each of the above-described at least one flute may consist of a straight flute extending in parallel with the axis of the body portion so that the above-described at least one cutting edge extends straight.
The above-described at least one flute preferably consists of at least two flutes so that the above-described at least one cutting edge consists of at least two cutting edges. Where the above-described at least one cutting edge consists of at least two cutting edges, the corrugated edge portion of each of the cutting edges is preferably formed such that the corrugated shape of the corrugated edge portion in each cutting edge is out of phase with that in any one of the cutting edges other than the above-described each cutting edge, as viewed in the axial direction of the cylindrical body portion. Described more specifically, it is preferable that a phase of the corrugated shape of the corrugated edge portion in each cutting edge is offset from that in one of the cutting edges which is circumferentially adjacent to the above-described each cutting edge, by an amount corresponding to a quotient of the pitch divided by the number of the cutting edges [by (pitch)/(number of cutting edges)]. This arrangement is effective to minimize parts of the workpieces which are left uncut due to the recesses of the corrugated shape, and accordingly improved the smoothness of the cut surface of the workpiece.
The pitch of the corrugated shape may be changed with a change of the diameter in a stepped manner, e.g., every pitch. Namely, the pitch may be changed in such a manner that the pitch is held constant within each pair of adjacent protrusion and recess while being changed between two pairs of adjacent protrusions and recesses. The other dimensions of the corrugated shape, i.e., the depth, first radius of curvature and second radius of curvature may be changed in a stepped manner, or alternatively, may be changed in a gradual manner such that these dimensions are changed even within each pitch. Further, the first radius of curvature and second radius of curvature can be changed in every protrusion or recess.
In the rotary cutting tool defined in any one of the fourth through sixth aspects of the invention in which the corrugated edge portion takes the form of the roughing cutting edge portion, if the pitch is changed, at least one of the depth, first radius of curvature and second radius of curvature is preferably changed together with the change of the pitch, so that all the protrusions and all the recesses providing the corrugated shape have substantially similar figures (i.e., figures substantially identical except for size). Each pair of protrusion and recess, which are adjacent to each other and cooperate with each other to constitute one pitch, may have respective radiuses of curvatures substantially equal to each other. However, the radiuses of curvatures of each pair of protrusion and recess do not have to be equal to each other but may be different from each other.
In the rotary cutting tool of each of the fourth through sixth aspects of the invention, the depth, first radius of curvature and second radius of curvature of the corrugated shape are preferably determined such that the following expressions (4)-(6) are satisfied:
0.05PRxe2x89xa6HRxe2x89xa60.5PRxe2x80x83xe2x80x83(4); 
0.2PRxe2x89xa6RR1xe2x89xa62.4PRxe2x80x83xe2x80x83(5); 
0.2PRxe2x89xa6RR2xe2x89xa62.4PRxe2x80x83xe2x80x83(6); 
wherein
PR represents the pitch of the corrugated shape;
HR represents the depth of the corrugated shape;
RR1 represents the first radius of curvature of the protrusion of the corrugated shape; and
RR2 represents the second radius of curvature of the recess of the corrugated shape.
In the rotary cutting tool of each of the seventh through ninth aspects of the invention in which the corrugated edge portion takes the form of the nicked cutting edge portion, the depth of the corrugated shape is preferably determined such that the following expression (7) is satisfied:
0.05PNxe2x89xa6HNxe2x89xa60.5PNxe2x80x83xe2x80x83(7); 
wherein
PN represents the pitch of the corrugated shape; and
HN represents the depth of the corrugated shape.
In the rotary cutting tool of any one of the third, sixth and ninth aspects of the invention in which the pitch of the corrugated shape is determined such that the above-described expression (1), (2) or (3) is satisfied, it is preferable that the pitch is set to be approximated to an amount obtained in accordance with the corresponding one of the following expressions (8)-(10). Namely, the pitch is preferably held within a range whose lower and upper limits correspond to the obtained amount minus 20% and the obtained amount plus 20%, respectively, as expressed in the following expressions (11)-(13).
P=1+(2/25)xc3x97Dxe2x80x83xe2x80x83(8); 
PR=1+(2/25)xc3x97Dxe2x80x83xe2x80x83(9); 
PN=1+(2/25)xc3x97Dxe2x80x83xe2x80x83(10); 
(1xe2x88x920.2)[1+(2/25)xc3x97D]xe2x89xa6Pxe2x89xa6(1+0.2)[1+(2/25)xc3x97D]xe2x80x83xe2x80x83(11); 
(1xe2x88x920.2)[1+(2/25)xc3x97D]xe2x89xa6PRxe2x89xa6(1+0.2)[1+(2/25)xc3x97D]xe2x80x83xe2x80x83(12); 
(1xe2x88x920.2)[1+(2/25)xc3x97D]xe2x89xa6PNxe2x89xa6(1+0.2)[1+(2/25)xc3x97D]xe2x80x83xe2x80x83(13); 
While the pitch of the corrugated shape is changed with the change in the diameter of the cylindrical body portion in the cutting tool of each of the third, sixth and ninth aspects of the invention, the pitch may be held fixed with the depth, first radius of curvature and/or second radius of curvature being changed with the change in the diameter of the cylindrical body portion in the cutting tool of each of the other aspects of the invention.
Where the cylindrical body portion of the rotary cutting tool has a portion in which the diameter of the cylindrical body portion is more than 50 mm, such a portion of the diameter more than 50 mm generally has a high degree of rigidity. Therefore, there is not a need for necessarily changing the pitch and other dimensions of the corrugated shape in such a portion having a high degree of rigidity. In view of this, it can be said that the present invention is advantageously applied to, particularly, a rotary cutting tool whose cylindrical body portion include a portion in which the diameter is larger than 50 mm.